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FORD-4S Product Details
TEMP:170° DIAM:54mm TYPE:Hot-side, Bypass
This premium thermostat has a larger heat motor/spring assembly for more precise temperature control along with a heavy-gauge chrome plated steel housing. 100% made in the USA.

Whether you are using an aftermarket radiator or not, this thermostat will provide the best possible heat dissipation from your setup and even deliver better overall performance than our competitor's 160° thermostats.  Reische believes the 170° opening temp is the ideal balance for high performance engines, providing high flow to your radiator by mid-180 temps while still providing good all season performance.  With proper fan settings your coolant temps in cool weather will be in the 170s and in hot weather the 180s, giving those running high levels of timing and/or boost added protection against engine-damaging detonation as well as maximum hp.

All Reische Performance thermostats ship with an OEM O-ring and are backed by a 5 YEAR WARRANTY.
2011-2014 F150 & Raptor 6.2L
2000-2005 Excursion 5.4/6.8L
2007-2010 Mustang GT 4.6L
1997-2014 Expedition/Navigator 4.6/5.4L
1996-2004 Mustang GT 4.6L**
1996-2019 E/F Series & Super Duty (gas)4.6/5.4/6.2/6.8L
1997-2010 F150 4.6/5.4/6.2L 1992-2011 Crown Vic 4.6L
**2005-2006 Mustang GT & 1996-2004 Mach 1/Cobra use Ford-4D
This thermostat fits many more vehicles- if you are unsure if this product fits your application then find your vehicle's Motorcraft thermostat (RT #) and use our Motorcraft Thermostat Cross Reference in our Application Guide.
Fan ECT1 High On: 190°
Low Fan Speed: 186° (shuts off @178°)
Fan ECT2 High On: 190°
High Fan Speed: 190°
Fan High Off: 186°
Fan Low Off: 182° (shuts off @180°)
Fan Low On: 184°
A retune is generally not required with use of our thermostats, however to get the best possible heat dissipation and most consistent temps, your fan settings should be lowered in your tune.  Otherwise a low temp thermostat will only be effective when the vehicle is moving because heat cannot be removed unless there is air passing through the radiator.  Unfortunately there are few programmers available at this time capable of modifying fan settings in most of the new Ford engine management systems.  The fan speed tables will need to be adjusted through a custom tune (available from most of our vendors) or via tuning software.  These new systems estimate coolant temps based on readings from a dry head temp sensor.  However these ‘inferred’ ECT values can be more volatile and may read as much as 8-10° hotter than actual coolant temps.  This means that a vehicle using our 170° thermostat could see ECT anywhere between 165-205°, depending upon conditions and fan settings.  We rely on your feedback, so please let us know if you become aware of any new developments in managing the fan settings for these applications.
Vehicle: 2002 Mustang 4.6L - Ford-4S - Roush Stg 1 Pkg - Test Date: Aug 12, 2009
Conditions: Engine @ operating temp, AC on/cooling fan on, hood open, ambient temps 93-97°
Sustained idle: ECT 174°, IAT 120°
Vehicle: 2002 Mustang 4.6L - **Motorcraft RT-1196** - Roush Stg 1 Pkg - Test Date: Aug 12, 2009
Conditions: Engine @ operating temp, AC on/cooling fan on, hood open, ambient temps 93-97°
Sustained idle: **ECT 190°**, IAT 120°
Note: 16° idle temp differential between OEM thermostat & Reische Ford-4S
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